Process of the electrolytic manufacture of chlorates and perchlorates.



NITED STATES ATENT OFFICE.

PROCESS OF THE ELECTROLYTIC MANUFACTURE OF CHLORATES AND PERCHLORA TESL SPECIFICATION forming part of Letters Patent No. 693,035, dated February 1 1, 1902.

Application filed July 19, 1901. Serial No. 68,942. (No specimens.)

T0 aZZ whom, it may concern.-

Be it known that I, PIERRE LoUIs EUGENE LEDERLIN,a citizen of the Republic of France, residing at Ohedde, pres Le Fayet, I-Iaute-Savoie, France, have invented a new and useful Improvement in or Relating to the Electrolytic Manufacture of Ohlorates and Perchlorates, which is fully set forth in the following specification.

The remarkable action of chromic acid,particularly when used in the form of chromates or bichromates as an auxiliary means in the manufacture of chlorates or perchlorates by electrolysis, is well known, owing to the experiments of Imhoff, and especially of Miiller and Broquet. From practical experiments it has been shown that the preliminary addition of a small quantity of these salts to the solution of chlorids or chlorates to be electrolyzed has the effect of considerably increasing the electrochemical reaction or yield, (grams of chlorates or perchlorates manufactured per ampere hour,) either of chlorates or perchlorates, as the case maybe,without, however, producing at the end of the operation any sensible diminution of the initial amount of chromic acid, and consequently without the consumption of this product. It is also known that with the same amount of chromic acid the increase of yield is substantially the same as when neutral chromate or bichromate is used. Finally, it is known that in the case of bichromate the solution, originally red, becomes gradually yellow, and returns slowly to the red color when the solution after electrolysis is left to itself; but these experiments have only been carried out in laboratories and the public trials have only lasted for some hours. If it is intended to apply the result of these experiments to practical use, the following conditions must be considered:

First, the cathodes should not be of platinum, like the anodes, but of a cheap material--as, for instance, iron, copper, brass, bronze, carbon, &c.which materials have the common quality of becoming attacked and more or less easily deteriorated in oxidizing solutions; second, the electrolyzed solutions should be used again after extracting by any convenient method the final product, (chlorate or perchlorate,) either by stopping the electrolysis when all the liquid has reached the maximum determined strength of perchlorate or chlrorate with the object of extracting the latter and again submitting the mother-liquors to electrolysis after having enriched them with the originalsubstance (chlorid or chlorate) or, on the other hand, when working continuously without interrupting the electrolysis by drawing off constantly or at certain intervals a quantity of liquid which, after having been deprived of the chlorate or perchlorate, is enriched with the original substance and again submitted to electrolysis. Under these conditions of working,beingthe only commercial ones,nothing abnormal according to the method used can beremarked during the first days or first operations. The cathodes are maintained in good condition, the liquids remain clear and of red-orange or yellow color, and the product is very high, close to the theoretical amount, which, for instance, is about 0.76 grams of potassium chlorate and 0.66 grams of sodium chlorate per ampere hour; but this soon decreases and falls to a figure close to the usual figure in the process without chromic acid. Finally, I have also discovered that the spontaneous and gradual return after electrolysis to the red color of an originally red liquid, which in the course of the electrolysis slowly turned yellow, take places slower and slower, and, finally, after a certain number of operations does not take place at all. This phenomenon is accompanied by a slow increase of the chlorometric strength, as well as of the alkaline strength, of the liquor, which were both zero at the beginning of the operation. Thus the chlorometric standard is completed by reaching six to seven grams of active chlorin per liter and remains stationary even after electrolysis has been stopped. At this moment the yield,which has progressively decreased, becomes stationary at about 0.35 grams to 0.45 grams per ampere hour in the case of chlorate of potassium, for example, instead of 0.70 grams at the commencement. I have also observed that the greater part of the cathodes of other material than platinum are slowly attacked and this more and more energetically during the electrolysis proper.

On interrupting the current by breaking the circuit a kind of violent ebullition takes place throughout the whole mass of the liquor. The

cathodes when withdrawn appear to be strongly corroded along their whole surface. Furthermore, I have discovered a general methodof maintaining the electrochemical yield at a maximum which at the same time allows the use of cathodes of such metal or alloy as is considered convenient. I have discovered that for this purpose it is sufficient to constantly maintain in a suitable manner the greater part, which may be taken to mean more than half or all of the chromic acid in the state of bichroinate and not of neutral chromate. The liquors remain clear and of a red-orange color. If the current is broken, Whatever the temperature may be at the moment no ebullition is observed. The cathodes of whatever the metal or alloy they may consist do not show any trace of alteration, and it the liquor had turned slightly yellow since the last breakage of the circuit it becomes instantly orange-red, and this state of things recurs indefinitely. Thus with a convenient amount of chromic acid and by using always the same liquors and the same cathodes a constant and very high yield is obtained, which introduce foreign salts.

can reach ninety per cent. of the theoretical amount, which result has never before been obtained. M0reover,this increase of the relative amount of bichromate can be obtained either during the electrolysis in cases of continuous operation or at the end of each operation in cases where the working is in successive operations.

The most simple process for maintaining the desired relative amount of bichromate consists in mixing the liquor with a very dilute solution of a mineral acid. The most convenient for this purpose is hydrochloric acid,asit can only form chlorids and does not The addition can be made either continuously or at certain intervals or at once after thestoppage of the electrolysis. I have, moreover, observed that this addition, which causesa troublesome liberation of chlorin gas, when solutions of chlorids or electrolyzed chlorates, which do not contain chromates or bichromates, are being operated upon, can be effected, on the contrary, very easily and without difficulty in the presence of these salts. Very considerable quantities of hydrochloric acid may, indeed, be introduced before liberating chlorin. In practice, however, a very small quantity is needed to renew the red color, and in all cases the chromic acid can be entirely brought back to the state of bichromate, which is the best course to follow, without'chlorin being liberated.

I have observed that the constant maintenance of chromic acid in the state of bichromate has such an effect on the yield that it is possible in the case of very soluble chloratessuch as, for example, chlorate of sodium- 130 push the electrolysis far enough to decompose almost all the chlorid, and thus to succeed in saturating the liquor with chlorate of sodium at the temperature of the electrolysis, while maintaining a very rich yield, and this without forming an appreciable quantity of perchlorate, so that it is possible to constantly withdraw from the electrolyzer a liquor saturated with chlorate of sodium at the desired temperature and allow it to deposit its chlorate by crystallization in suitable cooling apparatus, on the one condition that the corresponding quantity of chlorid is constantly supplied to the electrolyzer, thereby enabling chlorate of sodium to be manufactured in exactly the same manner as chlorate of potassium insteadof being obliged to effect an expensive and complicated concentration of the liquor containing it, as has been necessary up to the present time. Thus by my process liquors containing only one hundred and thirty to one hundred and fifty grams of NaCl,as compared with fourhundred and fifty to five hundred grains of NaGlO at centigrade, may be constantly withdrawn from the electrolyzer While obtaining a constant electrochemical yield of 0.55 grams of NaOlO per ampere'hour. WVithout the use of hydrochloric acid the yield falls under these conditions below 0.30 grams.

All that l have just said about very soluble chlorates is, moreover,applicable to very soluble perchlorates-such as, perchlorate of 'S0 (lium-by replacing the word chlorid by chlorate and the word chlorate by perchlorate. I have also established a remarkable fact in this connectionviz. at the same time that by the addition of hydrochloric acid the neutral chromate is brought back to the state of bichromate the strength of the electrolyzed liquor in active chlorin is decreased, so that the amount of active chlorin never attains one gram per liter during the elec-' trolysis, and even if the addition of acid is made to the liquor coming from the electrolyzer and while still hot, the active chlorin disappears completely in one or two hours that is to say, the chlorometric strength sinks to zero in the liquor when left to stand. This is another very considerable advan tage of my process, which thus spontaneously supplies a non-oxidizing liquor, and consequently suitable for use in the operations which the liquors have to subsequently undergo before returning them to the electrolyzer, and which enables receivers or conduits of any material to housed for this purpose. Finally, all these principles and processes are applicable to all electrolytic operations where it is necessary to utilize the action of chromic acid to increase the electrochemical yield. Thus in the preparation of bromates, iodates, 850., the same results are obtained by using the hydrobromic, hydriodic, &c., acids instead of hydrochloric acid.

I claim- 1. The process of electrolytically producing substances the yield of which is increased by the addition of chromic acid in suitable form to the solution to be electrolyzed, said process consisting in adding chromic acid in suitable form to a solution capable of yielding the desired substance, passing an electric current from an anode to a cathode through the liquid thus formed, and constantly maintaining the greater part of the chromic acid in the electrolyte in the state of bichromate during passage of the current.

2. The process of electrolytically producing substances the yield of which is increased by the addition of chromic acid in suitable form to the solution to be electrolyzed, said process consisting in adding chromic acid in suitable form to a solution capable of yielding the desired substance, passing an electric current from an anode to a cathode through the liquid thus formed, and adding a suitable mineral acid to the electrolyte to constantly maintain the greater part of the chromic acid in the electrolyte in the state of bichromate during passage of the current.

3. The process of producing chlorates or perchlorates from a solution capable of yielding the same, consisting in adding chromic acid in suitable form to said solution, passing an electric current from an anode to a cathode through the liquid thus formed, and constantly maintaining the greater part of the chromic acid in the state of bichromate during passage of therelectric current.

4, The process of producing chlorates or perchlorates from a solution capable of yielding the same, consisting in adding chromic acid in suitable form to said solution, passing an electric current from an anode to a cathode through the liquid thus formed, and adding a suitable mineral acid to the electrolyte to constantly maintain the greater part of the chromic acid in the electrolyte in the state of bichromate during passage of the current.

5. The process of producing chlorates or perchlorates from a solution capable of yielding the same, consisting in adding chromic acid in suitable form to said solution, passing an electric current from an anode to a cathode through the liquid thus formed, and adding hydrochloric acid to the electrolyte to maintain the greater part of the chromic acid in the electrolyte in the state of bichromate during passage of the current. I

6. The process of producing highly-soluble chlorates or perchlorates from a solution capable of yielding the same, consisting in adding chromic acid in suitable form to said solution, passing an electric current from an anode to a cathode through the liquid thus formed, constantly maintaining the greater part of the chromic acid in the state of loichromate during passage of the electric current and then cooling the electrolyzed liquor to deposit the chlorates or perchlorates in crystalline form.

In testimony whereof I have signed this specification in the presence of two subscribing witnesses.

PIERRE LOUIS EUGENE LEDERLIN.

Witnesses:

EMILE LEDRER, EDWARD P. MAOLEAN. 

